I think my guava tree is dying
My tree is a little over than a year old. I planted in March of last year and it bore fruit for the first time on or near October; just a couple, though. Now the tree is full of fruit but before they ripen, some are turning black and drying up. I also noticed a lot of ants up and down the trunk.
It sounds like your tree might have a fungus that affects as many as half the guavas in Puerto Rico. Unfortunately, there is no cure. The best treatment is optimum cultural practices, so your tree will be healthy enough to ward off disease and pests, remove and destroy any fruits or leaves as soon as they show a sign of disease. Also, your tree is very young, so do not stress it by leaving it full of flowers and fruit. The best idea is to remove at least 1/2 the flowers before they are pollinated, and then remove 1/2 the fruit that sets. This way, the tree has energy left to devote to growing roots and leaves, and developing its defense systems. Here is an article that will help you grow a healthy guava: https://www.gardeningknowhow.com/edible/fruits/guava/growing-guava-fruit-trees.htm
You might get in touch with the University of Puerto Rico Dept of Horticulture for more information.